Patent GB-931125-A (GB)
Title: Object detection apparatus
IPC: G01S7/527
Filed: 1959-11-17
Abstract: 931,125. Traffic detectors. GENERAL RAILWAY SIGNAL CO. Nov. 17, 1959 [April 24, 1959], No. 38938/59. Class 118. [Also in Groups XIX and XL (c)] Apparatus for detecting the presence of an object at a predetermined position comprises means for directing energy towards that position, energy receiving means arranged to provide a first output in response to that energy when received in the presence of an object at that position and to provide a second output, different from the first output, in response to that energy when received in the absence of an object at that position, and means for indicating detection of an object in response to the occurrence of both of the outputs wherein discrimination between successive objects at that position is dependent on the occurrence of one of the outputs between two occurrences of the other of the outputs. The embodiment utilizes ultrasonic pulse-echo technique with directive transducers and is applied to counting the number of cars in a parking garage, Figs. 1A, I B, and to counting the number of cars, and of lorries, passing a point on the highway, Fig. 1C, ID; in the former case discrimination against persons and the like is effected by making the valves controlling " ground " and " vehicle output relays responsive only if the series of corresponding echo trains are continuous over many pulse repetition periods, and multiple reflections between vehicle and garage ceiling are inhibited by covering the latter with soundabsorbent material, Figs. 15A, B (not shown); a differential counter subtracts the vehicles passing an exit path from those passing an entry path and in a multi-storey parking garage a central office houses a common transmitter and the receivers &c. Separate transmitting and receiving transducers may be replaced by a single transducer connected via a hybrid transformer duplexer, Fig. 12 (not shown). The parking garage detection system comprises the units shown in Fig. 2, corresponding waveforms being depicted in Figs. 8A, 8B. A blocking oscillator pulse generator produces repetitively 1 ms. pulses a (see also Fig. 3, not shown), which key a 20 kc/s. oscillator (see also Fig. 4, not shown), and trigger the gate timing circuits. Waveform d determines the maximum height of detectable vehicle and its trailing edge produces the " V " (vehicle) gate pulse g of width sufficient to cater for all heights of cars. The trailing edge of the V gate pulse produces j the trailing edge of which produces the " G " (ground) gate pulse m. The gate pulses and the echo pulses are fed to the counter-control circuit, Fig. 7. Assuming that no car is present the receiver output p effects waveform r at valve V6G output and a train of such pulses, Fig. 8C, is integrated by circuit 32 ... 37, waveform u, and relay RG is de-energized to prepare via contact 46 the counter 50 for energization when a similar sequence of events subsequently arises as a car enters the ultrasonic beam and relay RV is de-energized to close contact 47. The circuit arrangement ensures that a car with a fabric, i.e. sound-absorbing, top is not counted twice. For highway vehicle counting in car and lorry categories the system incorporates a third gate, Figs. 13, 14A, 14B (none shown).